Power consumption is an ever increasing concern in analog circuit design. As the transistor size shrinks, it is increasingly difficult to reduce power at the same scale. Standard methods of designing power efficient circuits are becoming limited and new methods of extending power savings of analog circuits must be used to further scale power supply and consumption with process scaling.
In general, analog circuits are optimized to support all process, voltage, and temperature (PVT) conditions and operating configurations. Examples of operating configurations include but are not limited to frequency, impedance ranges, reference voltage range, temperature ranges, and bias ranges. Configuration registers, fuses, and compensation circuits are used to narrow the operating focus of the analog circuit, however, these mechanisms for compensation are limited.
Compensation circuits are often redundant, complex, and consume large amounts of area. Compensation circuits such as resistance compensation use a replica circuit and a sensing mechanism to create feedback that is used by a Finite State Machine (FSM) to trim the analog circuit. These and similar specialized compensation circuits for fixed functions are typically instantiated in multiple places for multiple circuits and are redundant. Additionally, the FSMs are often complex and are difficult to validate because of their mixed signal nature.
Fusing is a relatively simple way of trimming an analog circuit by providing fixed process skew data to the analog circuit. The fuses are determined at the factory during High Volume Manufacturing (HVM). While fusing is an effective and simple way to improve analog circuit operating focus, it lacks the information regarding the temperature and voltage sensitivity over time. Voltage and temperature are important parameters in circuit performance, so there is a lot of critical trimming data that is missed through this method alone.
Configuration registers are also used to trim analog circuits. Configuration registers are static in nature, so they also suffer from lack of real time voltage and temperature feedback. Using traditional circuit trimming techniques for analog circuits result in a higher power and more complex design to cover a wide range of PVT conditions and operating configurations.